MicroRNAs (miRNAs) are a class of non-coding RNAs that function as endogenous triggers of the RNA interference pathway. Originally discovered in Caenorhabditis elegans, this group of tiny RNAs has moved to the forefront of biology. With over 300 miRNA genes identified in the human genome, and a plethora of predicted mRNA targets, it is believed that these small RNAs have a central role in diverse cellular and developmental processes. Concordant with this, aberrant expression of miRNA genes could lead to human disease, including cancer. Although the connection of miRNAs with cancer has been suspected for several years, four recent studies have confirmed the suspicion that miRNAs regulate cell proliferation and apoptosis, and play a role in cancer.